Microwave film dryer

ABSTRACT

This disclosure relates to apparatus for drying photographic film, following developing, with microwave energy. The film is supported for movement, during spaced time intervals, through a plurality of portions of an extended waveguide, and a dummy load is located at the end of the waveguide.

Umted States Patent m1 3,582,597

[72] Inventor Peter H. Smith 3,474,213 10/1969 Hilton etal. 219/1055 Chicago, Ill. 3,500,012 3/1970 Hilton 219/1055 I; 1 rw N0 2 1: FOREIGN PATENTS l l e 8' v 1 Patented June l 1971 1,050,493 12/1966 Great Britain 219/1055 [73] Assignee Reeve Eleclronics,lnc. P imary Examiner-1V. Truhe Chicago, Ill, Assistant Examiner-L. H. Bender Attorney-Pendleton, Neuman, Williams & Anderson [54] MICROWAVE FILM DRYER 10 Claims, 3 Drawing Figs. [52] U.S.Cl 219/1055, 219/ 10.61 [51] int. Cl HOSb 9/06,

H05b 5/00 50 Field of Search 219 1055, AB$TRACT= This disclosure relates to apparatus for drying 01, photographic film, following developing, with microwave [56] References Cited energy. The film is supported for movement, during spaced time intervals, through a plurality of portions of an extended UNITED STATES PATENTS waveguide, and a dummy load is located at the end of the 3,463,894 8/1969 Bleackley 219/ 10.55X waveguide.

MICROWAVE FILM DRYER The present invention relates to a dryer for photographic film, and specifically to such a dryer employing microwave energy. it is necessary to dry photographic film as the last step of the developing process. Present methods of accomplishing this drying take a relatively long time, and require considerable space when a large quantity of film is to be dried at the same time. It is desirable to minimize both the time required to perform the drying process and the space required by the film during the drying.

Accordingly, one of the principal objects of the present in vention is to provide a film dryer in which the film is dried in a relatively short time, within a very small volume of space.

This and other objects and advantages of the present invention will become manifest upon examination of the following description and the accompanying drawings.

in one embodiment of the present invention, there is provided a source of microwave energy, a waveguide connected to said source for receiving said energy, said waveguide being formed between a pair of parallel spaced plates and defined by a plurality of wall members secured to said plates for conveying said microwave energy along an extended path between said plates, means secured to said plates and juxtaposed with opposite ends of said wall members for reflecting said energy at least partially along the length of said extended path, and means for supporting a length of photographic film for a continuous movement through said waveguide.

Reference will now be made to the accompanying drawings, in which:

FIG. 1 is a side elevation of one of two similar sections making up an exemplary embodiment of the present invention;

FIG. 2 is a perspective view of a portion of an exemplary embodiment of the present invention, shown in partially open condition and including the section illustrated in FIG. 1; and

FIG. 3 is an enlarged end view partly in cross section of a portion of an exemplary embodiment of the present invention, shown in closed condition.

Referring now to the drawings, the film dryer apparatus includes a waveguide defined partly by a pair of conductive plates and 12. The plates are preferably formed of aluminum, but any other conductor may be substituted therefor, and well understood in the art. Spacer members 14 and 14 interconnect the plates 10 and 12 with a hinge 15. The hinge 15 permits the plate 12 to swing away from the plate 10, thereby to expose and make accessible the interior regions ofthc dryer apparatus. A series of wall members 16 to 23 are secured to the plate 10, and a similar series of wall members are secured to the plate 12 at corresponding positions, so that when the plates are closed into parallel relationship the walls form portions of the extended waveguide in the form of channels defining a serpentine path between the plates 10 and 12.

Each of the wall members 16 to 23 comprises an L-shaped member having a flange or lip 24 secured to the plate 10 by means of solder or the like (FIG. 3). The walls 16 to 23 are all disposed in parallel relation and are equally spaced apart on the plate 10. A plurality of end wall members 26 to 28 and 30 to 32 are interconnected at both ends with one end each of the wall members 16 to 22, to form a continuous serpentine path for the waveguide. The upper ends ofithe wall members 16 and 17 are connected to an extension 34 which protrudes outwardly beyond the edge of the plate 10 and terminates in a flange 36. The flange 36 is adapted to be connected to a waveguide leading to a microwave source, so that microwave energy may be introduced into the waveguide through the extension 34. The microwave energy passes downwardly between the wall members 16 and 17 and, at the bottom of this space, is transferred by the end wall member 26 to the space between the wall members 17 and 18. The energy travels upwardly in this space, and, at the top, is transferred by means of the end wall member 30 into the space defined between the wall members 18 and 19. The microwave energy is thereafter conducted, in similar fashion, successively through the spaces defined by adjacent pairs of the wall members 16 to 23. The final space, defined between the wall members 22 and 23, terminates with a plain end wall member 29.

A dummy load 38 is located at the bottom of the space between the wall members 22 and 23. The load 38 is wedge shaped with its apex oriented upwardly, toward the direction from which the microwave energy enters the space between the wall members 22 and 23. The load 38 is comprised of relatively lossy dielectric material, so that microwave energy is absorbed by the dummy load 38. A thermostatic switch 40, mounted on the wall member 23, is juxtaposed with the dummy load 38 and is operable in response to a temperature in excess of a predetermined value. The purposeof the thermostatic switch 40 is to provide a signal to deenergize the source of microwave energy whenever the temperature of the dummy load exceeds the predetermined value, to prevent overheating the load 38, and to prevent damage to the microwave source.

Preferably, the loss factor of the dummy load 38 is not as great as that of the moisture to be dried from the film passing through the dryer, so that when wet film is present within the dryer, the film absorbs substantially all of the microwave energy entering the waveguide in vaporizing the moisture, and the load 38 remains cool. The dummy load 38 does, however, absorb substantially all of the microwave energy entering the waveguide which is not absorbed in drying the film. The wedge shape of the dummy load 38 tends to trap any microwave energy which reaches it, and tends to prevent reflection of the energy back toward the source. It is highly desirable to minimize this reflection because reflected energy combines with the energy traveling forward within the waveguide to produce standing waves within the waveguide and to produce the unwanted condition in which there is substantially less drying effect at some portions of the waveguide than at others, Reflected energy which reaches the source of the microwave energy is undesirable in that it tends to damage the microwave source if permitted to exceed a given limit.

Each of the ends wall members 26 to 28 and 30 to 32 is made up of three sections, namely, a center section 41 and two side sections 42 and 43. The center section 41 of the end wall member 26 is aligned across the direction of the wall 17, and is spaced slightly therefrom. The side sections 42 and 43 connect opposite ends of the center section 41 with the lower end of the wall members 16 and 18. The three sections 41 to 43 are provided with flanges 44, by which they are bolted to the plate 10. The side sections 42 and 43 are about 50 percent longer than the center section 41, and are disposed at an angle to both the center section 41 and the wall members 16 and 18 to which they are connected. When the side sections 42 and 43 are formed at an angle of 45 relative to the center section 41, energy is most efficiently transferred from thespace on one side of the wall 17 to the space of the other side of that wall.

The end wall members 27, 28 and 30 to 32 are all formed identically to the end wall member 26, so that each of them efficiently transfers microwave energy progressively along the waveguide. The end member 29 is formed of a single section closing the end of the space between the wall members 22 and 23, and forming a right angle with those wall members, and supports the dummy load 38.

The waveguide which has been described with. reference to FlG. 1, is duplicated in mirror image on the interior surface of the plate 12. Wall members 16' to 23' are attached to the plate 12, corresponding to each of the wall members 16 to 23 of FIG. 1, and the ends of the corresponding wall members join each other midway between the plates 10 and 12, when those plates are in parallel condition, as illustrated in FlG. 3.

A plurality of end wall members 26' to 32' are provided on the interior surface of the plate 12, and they correspond, in mirror image, to the end wall members 26 to 32. Both sets of end wall members extend away from their respective plates a slightly less distance than do the wall members 16 to 23 and 16' to 23'. As a result, narrow gaps are formed between the inner edges of the two sets of end wall members. it is through these gaps that the film to be dried enters and leaves the waveguide, as illustrated in FIG. 3.

In FIG. 2 it is illustrated how the film is supported during its passage through the waveguide. A plurality of reels 45 to 48 are supported in fixed relationship above the end wall members 30 to 32. The reels 45 to 48 support lengths of film 49 to 52, respectively, which pass through adjacent sections of the waveguide defined between the plates and 12. The fronts of the reels 45 to 48 are aligned with the gaps between the end wall members secured to the plates 10 and 12, so that film can hang from the reels 45 to 48 and pass through the appropriate gaps.

The backs of the reels 45 to 48 are disposed behind the rear surface of the plate 10. An additional set of reels (not shown) is disposed at the bottom of the dryer assembly, and the film lengths 49 to 52 are guided at their lower ends by the additional reels. The film lengths 49 to 52 are all portions of a single continuous length of film, and each portion of the film to be dried occupies the positions of the film lengths 49 to 52 successively as it makes multiple passes through the dryer. Wet film enters the apparatus by means of the reel 45 and proceeds upwardly through the space shown occupied by the film length 49. When it reaches the lower end of the dryer assembly, it is transported by another reel (not shown) and passes upwardly behind the plate 10 to the reel 46. The reel 46 transports the film and passes it downwardly through the space shown occupied by the film length 50. Thereafter, the film being dried travels downwardly along the portion of the waveguide shown occupied by the film lengths 51 and 52, respectively. It then passes out of the dryer apparatus in virtually completely dry condition. Each portion of the film being dried thus makes four passes through various portions of the waveguide during drying.

Apparatus embodying the present invention is capable of drying 16 mm. film at the rate of 50 feet per minute, with approximately l kilowatt of microwave power. It is preferable to use a leader and a trailer at the beginning and trailing edges of the film to be dried, to insure that all of the film to be dried occupies the waveguide for approximately the same length of time. Even quality of the resulting film is thus assured.

lt is important to prevent the microwave energy within the waveguide from escaping inadvertently, in order to maintain the efficiency of operation of the apparatus and to minimize radiation hazards for nearby personnel. Accordingly, a microswitch 50 is mounted on the plate 10, and has an actuator 52 for engaging the plate 12 when the latter is swung into closed condition. Two cooperating portions 54 and 56 of a latch mechanism are mounted on the plates 10 and 12 to hold them in closed position. When the actuator 52 of the microswitch 50 is engaged, the switch is closed, producing an electrical signal which is used to permit the microwave source to be energized. While the dryer apparatus is opened, during film loading or inspection, the switch 50 opens and thus prevents the operation of the energy source. Moreover, the two sections of the flange 36 are bolted to a single mating flange (not shown) connected with the waveguide leading to the microwave source, so that the apparatus is held in its closed condition whenever all of the bolts are in position in the flange 36. The gaps through which the film lengths 49 to 52 pass into and out of the waveguide are sufficiently small and narrow as to substantially prevent any escape of microwave energy.

The dummy load 38 is preferably formed by casting a concrete mixture into the required wedge shape. A quantity of powdered graphite is mixed into the concrete and the entire casting is reinforced with wire mesh to reinforce the concrete against the stresses caused by rapidly changing temperature. Preferably, a plurality of bolts 60 are cast into place when the casting is formed, and the bolts 60 extend through aligned apertures in the lower walls 29 and 29, where they are held in position by nuts 62. The purpose of the graphite is to make the resistivity of the dummy load about 100 ohms per cubic centimeter in one preferred form of the present invention.

What I claim is: p 1. In apparatus for drying web material, the combination comprising a source of microwave energy means defining a microwave waveguide for conveying microwave energy from said source along an extended path, means for supporting said web material for continuous movement through said waveguide, a dummy load located at an end of said waveguide, and thermally responsive meansjuxtaposcd with said load and operative to provide a control signal to deenergize said source of microwave energy in response to the temperature of said load exceeding a predetermined value.

2. Apparatus according to claim 1, wherein said dummy load comprises a wedge-shaped section of material having a relatively high dielectric loss.

3. Apparatus according to claim 1, wherein said supporting means comprises means enabling each portion of said web material to move through said waveguide during a plurality of spaced time intervals.

4. Apparatus according to claim 1, wherein said waveguide is formed in two sections connected together by a hinge, the interior of said waveguide being made accessible by swinging said sections apart.

5. Apparatus according to claim 4, including latch means for releasably holding said two sections together and at least partially closing the opening therebetween to prevent the escape of microwave energy from within said waveguide.

6. Apparatus according to claim 5, including means for sensing and indicating when said two sections are in closed relation.

7. Apparatus according to claim 4, wherein said waveguide is formed between two parallel plates and is defined by a plurality of parallel wall members secured to said plates, said wall members extending into the space between said plates and joining with corresponding wall members midway between said plates.

8. Apparatus according to claim 7, including a plurality of end wall members secured to said plates and interconnecting alternate ones of said wall members, said end wall members extending into the space between said plates, the inner edges of said end wall members being spaced apart midway between said plates.

9. Apparatus according to claim 8, including means for supporting said web material for movement through the space between the inner edges of said end wall members.

10. Apparatus according to claim 9, including a plurality of rollers for supporting said web material and enabling said web portions of said waveguide. 

1. In apparatus for drying web material, the combination comprising a source of microwave energy means defining a microwave waveguide for conveying microwave energy from said source along an extended path, means for supporting said web material for continuous movement through said waveguide, a dummy load located at an end of said waveguide, and thermally responsive means juxtaposed with said load and operative to provide a control signal to deenergize said source of microwave energy in response to the temperature of said load exceeding a predetermined value.
 2. Apparatus according to claim 1, wherein said dummy load comprises a wedge-shaped section of material having a relatively high dielectric loss.
 3. Apparatus according to claim 1, wherein said supporting means comprises means enabling each portion of said web material to move through said waveguide during a plurality of spaced time intervals.
 4. Apparatus according to claim 1, wherein said waveguide is formed in two sections connected together by a hinge, the interior of said waveguide being made accessible by swinging said sections apart.
 5. Apparatus according to claim 4, including latch means for releasably holding said two sections together and at least partially closing the opening therebetween to prevent the escape of microwave energy from within said waveguide.
 6. Apparatus according to claim 5, including means for sensing and indicating when said two sections are in closed relation.
 7. Apparatus according to claim 4, wherein said waveguide is formed between two parallel plates and is defined by a plurality of parallel wall members secured to said plates, said wall members extending into the space between said plates and joining with corresponding wall members midway between said plates.
 8. Apparatus according to claim 7, including a plurality of end wall members secured to said plates and interconnecting alternate ones of said wall members, said end wall members extending into the space between said plates, the inner edges of said end wall members being spaced apart midway between said plates.
 9. Apparatus according to claim 8, including means for supporting said web material for movement through the space between the inner edges of said end wall members.
 10. Apparatus according to claim 9, including a plurality of rollers for supporting saId web material and enabling said web material to move in a continuous path through a plurality of portions of said waveguide. 